8.4 Anonymous Types

Let’s go through anonymous types in C# — a handy way to create lightweight objects without defining a class.

---

📌 1. What Are Anonymous Types?

• Anonymous types are objects created on the fly without explicitly declaring a class.

• Useful when you need a temporary object to hold some data.

• Properties are read-only.

• Type is inferred by the compiler.

---

📌 2. Syntax

var obj = new { Property1 = value1, Property2 = value2 };

• Use var (type inference)

• Property names and values are defined inline

---

📌 3. Example

var person = new { Name = "Alice", Age = 25 };
Console.WriteLine(person.Name); // Alice
Console.WriteLine(person.Age);  // 25

• No class Person needed

• Properties Name and Age are read-only

---

📌 4. Using Anonymous Types in LINQ

Anonymous types are commonly used in LINQ for projection:

var students = new[]
{
    new { Name = "Alice", Age = 20 },
    new { Name = "Bob", Age = 22 }
};
 
// Select only names
var names = from s in students
            select new { s.Name };
 
foreach (var n in names)
    Console.WriteLine(n.Name); // Alice, Bob

• Avoids creating a separate class just to hold the projected data

---

📌 5. Limitations of Anonymous Types

Limitation	Explanation
Read-only properties	Cannot modify after creation
Cannot be used as method return type (unless var or dynamic)	Type is compiler-generated
Cannot inherit from other classes	They are sealed by default
Only useful locally	Not ideal for public API return values

---

📌 6. Advantages

1. Quick and lightweight objects

2. Great for temporary data storage

3. Perfect for LINQ projections

4. No need to clutter code with small class definitions

---

📌 7. Example: Multiple Properties in LINQ

var students = new[]
{
    new { Name = "Alice", Age = 20 },
    new { Name = "Bob", Age = 22 }
};
 
var result = students.Select(s => new { s.Name, IsAdult = s.Age >= 21 });
 
foreach (var r in result)
    Console.WriteLine($"{r.Name} - Adult: {r.IsAdult}");

Output:

Alice - Adult: False
Bob - Adult: True

• Added computed property IsAdult in the anonymous type

---

📌 8. Summary Table

Feature	Description
Syntax	var obj = new { Prop1 = val1, Prop2 = val2 };
Properties	Read-only, compiler-inferred types
Common Use Case	Temporary objects, LINQ projections
Limitations	Cannot modify, cannot inherit, limited scope
Advantage	Quick, concise, no extra class needed

---

✅ Tip:

• Use anonymous types when you need a quick object for short-term use, especially inside LINQ queries.

• For long-term or reusable objects, define a named class instead.